With the development of circuit technologies, the use of programmable devices is becoming more and more widespread. The programmable devices like a piece of paper or a pile of building blocks, and engineers can design a digital system freely through a traditional schematic input method or a hardware description language. The correctness of the design can be pre-verified through a software simulation. After implementing a Printed Circuit Board (PCB), online modification capabilities of the programmable device can further be used to modify the design at any time without modifying a hardware circuit. Developing digital circuits with the programmable devices can greatly shorten design time, reduce PCB area and improve reliability of the system.
A designer converts a function to be implemented into a form of a schematic diagram or the hardware description language, compiles it by a compiling software, and downloads the compiled program into the programmable devices through a JTAG interface, and the programmable devices will operate in accordance with an intent of the designer.
The JTAG is an international standard protocol, which is mainly used for a chip internal test and program download. Now, almost all of the programmable devices support the JTAG interface, and the programmable device with the JTAG interface is referred to as a JTAG programmable logic device. A standard JTAG interface includes the following pins:
JTAG_TMS: a mode selection pin;
JTAG_TCK: a clock pin;
JTAG_TDI: a data input pin;
JTAG_TDO: a data output pin;
JTAG_RST_N: a JTAG reset pin.
At present, the common method for downloading by the JTAG programmable logic devices is:
Using a JTAG download cable to connect a serial port of a PC (computer) and the JTAG interface of the JTAG programmable logic device, running a JTAG download software on the PC, and downloading a compiled file of the programmable device which has been compiled into the JTAG programmable logic device through the JTAG download cable. The commonly-used JTAG download method mainly has the following defects:
A. as the JTAG interface does not support hat plug, after the download is implemented, if the JTAG download cable is directly unplugged from the JTAG connector of the JTAG programmable logic device, the JTAG interface is very easy to be damaged, leading to the JTAG programmable logic device not performing subsequent program upgrade functions;
B. the JTAG download requires to directly connect the serial port of the PC and the JTAG interface of the JTAG programmable logic device through the JTAG download cable; as the JTAG apparatus where the JTAG interface is located is possibly not grounded or not well grounded, leading to that a large amount of static electricity is accumulated on the apparatus, and when the JTAG programmable logic device of the apparatus performs the download through the JTAG download cable, the large amount of static electricity accumulated on the JTAG apparatus will be transmitted to the serial port of the PC through the JTAG interface, and eventually burn out the serial port of the PC, leading to that the download can not be performed;
C. in addition, the upgrade is comparatively troubled, and if the JTAG apparatus which is already put on the market and is sold to a user is required to upgrade the JTAG programmable logic devices, related staff needs to hold the JTAG download cable to the site of the apparatus to be tested of the user, open the apparatus to be tested, and then connect the JTAG connector connected with the JTAG download cable to the JTAG apparatus and the PC respectively, and manually download an upgrade program, which is liable to affect normal operations of the JTAG apparatus of the customer, and is time-consuming and laborious and extremely inconvenient.